SR20 SAFC tuning

[SRSmith]

Yep, I know there are a million threads on this. Trust me, I've read them.

And that's why I'm confused. my inputs are far different from any that other people are using.

I'm using:
SR20 redtop
300zx maf
480 cc injectors
t3t4 turbo
apexi safc 2

For the 300 maf, I am usining a 2 in 6 out setting. Most people use the safc with the more common 550cc injectors. They recommended starting with a -33% setting on both the high and low throttle. As my 480cc injectors are somewhat in between the stock 370 and common 550, I set the unit at -15%.

To my surprise, I'm running lean. So I immediately shut it off and set it to -5%. I'm still a bit lean even with the cold start, so I set it to +10%. Now I'm running around 12.5 afr, but as it warms up the motor creeps into lean territory again.

For a random detail - when I unplug the maf, I'm running a good air/fuel ratio. I expected to be running rich as I have bigger injectors now.

Are my inputs correct? Are these the expected outputs for my settings? And if not, is it possible my ecu has some unknown tune that is screwing me?

As always, I appreciate the support. :hug:

[RalliartRsX]

Toss that piece of shit in the fucking trash

Seriously....

[Kingtal0n]

300zx maf goes with Apexi Power FC and 740CC Injectors to take care of that turbo


If you wanted to use SAFC with that turbo it needs to be on the OEM MAF sensor, with 550cc injectors, and the max boost will be approx 14psi (340rwhp~ max?)

Anything smaller than 550cc is for stock size turbocharger. Even S15 stock turbo uses 4xxcc so just imagine going from T-25 to T3 size 4xx isn't going to cut it.

SAFC cannot adjust engine timing so the motor will probably eat rod bearings even with the A/F dialed in properly. That is why he says "Trash it" because even though it can tune the A/F properly the engine's advanced, stock ignition timing can still ruin your engine.

In other words, when you use SAFC to remove fuel (-xx%) the OEM computer is going to ADD TIMING in response. So the larger the injector is, the more fuel you remove, the more timing gets added. Additional timing is unwanted and the OEM computer has no idea you are using a SAFC to remove fuel so it thinks you are reducing boost pressure (-xx%) when in reality you are increasing boost pressure.

Tuning wise. It is necessary to use heat range 7 NGK plugs and an aftermarket, low lift(lowest lift), long duration (260-270*)camshaft or you are wasting time.

0. Before tuning, Remove some base engine timing at the crankshaft by retarding at the CAS. Remove approx 2-3* minimum. You may even wish to remove a bit more. This will help protect the engine from the excess timing an SAFC will add, at the expense of fuel economy cruising (you may lose a couple MPG)

1. You must unplug the factory O2 sensor before trying to tune an SAFC.
2. Aim for 14.7 to 15.2:1 (slightly lean) for all cruise and near idle.
3. Aim for 11.2 to 11.5 for all boost over 10-12psi
Never go above 12.2:1 in boost
Never go below 14.4:1 in cruise/idle (anything below say 14.2:1 air fuel ratio will foul plugs, carbon coat piston/valve/chamber, it allows a brittle hard diamond-like carbon coating to persist in every recess and may over time lead to engine damage, cylinder wall scarring, hot spots, even chunks can break off and damage the turbine)

[SRSmith]

This is some great information. I appreciate the detail.

So for starters, my injectors are too small. Does the fact that im adding +10% make this apparent. am i causing them to run above full duty cycle? Obviously this is dangerous.

[SRSmith]

Am I able to use this t3t4 turbo with stock cams?

Im looking at some enthalpy tuned ecus locally. Both use 550cc injectors, 300zx maf, stock cams, and one is set for a t28 and the other for a gt35. Id have to send either in to get them reflashed.

[Kingtal0n]

waste of time fooling with stock cams on a sr20det

if you want to use the stock cam, use the stock ECU, injectors, and turbo. No point complicating the setup with injectors, tuning, large turbo when you've got the engine airflow limited with the OEM camshaft.

OEM cam will work but its like you are tuning to only use 3 of the 4 cylinders

[SRSmith]

What cams do you recommend then? Wasn't expecting to buy these and I know there are a lot of opinions as well as options.

[Kingtal0n]

get brand new JWT S3 or similar. Low lift with 264+ Duration
You can use Tomei or Greddy or HKS Low lift 264+ Duration

Get the matching springs for the cam. Greddy cam = Greddy springs. They will recommend a spring. If the cam manufacturer says stock will work then its up to you. But don't mix and match springs. Don't try BC or Comp cam springs with a JWT or greddy camshaft.

Just forget the cam if you are inexperienced and need to get the car running. The cam is for performance and you seem like you just need the engine to run properly.

That is why I suggest stock ECU/inj/turbo

[SRSmith]

Well, stock parts aren't in the cards anymore. I suppose I could use the current setup with 550cc and tuned ecu? Would have to run low boost.

[Kingtal0n]

I Would keep looking in ebay for a used Power FC

I got them before for $350

A rom tune still requires an SAFC. A power FC can work without an SAFC.
Therefore the price of Power FC is similar to ROM tune + SAFC and far more powerful.

These days using a high quality fuel injector you really want at least double size. So if you calculated that you need a 550cc then you should use a 1000cc injector instead. This way duty cycle is low (near 50-60%) at peak power, this will ensure more fuel is being sprayed during the appropriate window (valve event) and also keep the injector driver cooler.

So in the end using 550cc injectors and stock cams is "doing it wrong" you really need 700-1000cc injectors, 264+ low lift cams, and a fully tunable Stand-alone Power FC or similar

[SRSmith]

I've found a couple FC for good prices. However, I'm stumped by this SAFC so i doubt I'll do better with a Power FC.

We have several reputable tuners around here. Unfortunately, all of them are specialize in WRX's. Guess that's to be expected in Wisconsin.

[LoSt180]

A rom tune absolutely negates the need for a SAFC. A tune sets up the calibration to properly use the Z32 MAF and the injector size being used. If you're combining a tune with a SAFC, you're doing it wrong.


To my surprise, I'm running lean. So I immediately shut it off and set it to -5%. I'm still a bit lean even with the cold start, so I set it to +10%. Now I'm running around 12.5 afr, but as it warms up the motor creeps into lean territory again.


The ECU has cold temperature enrichment tables, so make sure the engine is fully warmed up before you "tune" that SAFC. What do you consider lean here also? Are you running 12.5 at idle or full boost? You should be seeing stoic (14.7) at idle when the engine is warmed up, 12.5 at warm idle is dumb rich.

I've found a couple FC for good prices. However, I'm stumped by this SAFC so i doubt I'll do better with a Power FC.


Your setup isn't that complicated, normal Z32 MAF with S15 injectors. You can email Martin an RSEnthalpy and he can most likely sort out a tune for you easily. Would be WORLDS better than trying to screw around with a SAFC like it's 2001 all over again.

Here's some more technical info on why that SAFC should be trashed: With larger injectors, you need to reduce the injector pulse width to deliver the same amount of fuel. The ECU uses something called a load scale table to help determine a pulse width at a given RPM/load combo. Load is primarily determined by the MAF reading. There's a bunch of math involved and other factors, but I'm keeping it simple here.

These are made up numbers to show the theory/point here:
At 4500 rpm and a load of 100 (full throttle) the ecu will command a pulse width of 20 to deliver a certain amount of full.
Now, with larger injectors a pulse width of 20 will inject too much fuel. What you really need is a pulse width of 15 to deliver the same amount of fuel as the factory injectors.
The SAFC will change the MAF reading so that at full throttle at 4500 rpm, the ECU will "see" a load of 75 and command a pulse width of 15.
Okay, your fueling is "correct" but here's where the whole thing falls apart: the ECU uses a load scale for a bunch of other things, including (as pointed out already) timing tables. At a given RPM, timing can be 3-7 degrees advanced when going down from 100 to 75 on the load scale. So at 4500 rpm and a load of 100, timing is 12*, but at a load of 75, timing is 18*.

Plus, you're now not even using the last cells in the tables that are indexed to load because that SAFC is tricking the ECU to only ever see a max load of 75. So you took a 16x16 table and limited it to 16x12. Effectively losing granularity and control in the ECU.

A proper rom tune (or standalone) will adjust the math on the ECU itself so that your MAF reading reflects an accurate load value and injector pulse widths are calculated correctly, accross the full table size. Once the ECU is calibrated correctly to your setup, any outside modifiers (aka SAFC) are not needed and will interfere with proper operation.